The use of batteries to power electronic devices and systems is ubiquitous today. When used in consumer products such as handheld electronic devices, or larger systems such as wireless camera networks, for example, batteries must provide power for extended periods of time and do so in a safe and reliable manner. Care must be taken, however, when using multiple batteries in parallel and/or in series to form a battery pack. For example, many types of battery cells, such as certain types of Lithium cells, are prone to over-heating and catching fire if one or more cells in the battery pack are mismatched, defective or damaged. One common solution to protecting against cell fires is to design a battery pack with internal protection mechanisms such as preventing replacement of individual cells, resettable fuses, etc.
As another measure to minimize the risk of faulty battery packs, manufacturers carefully select batteries that match in voltage (when cells are used in parallel) and in capacity (when cells are used in series). The matched cells are then assembled in a respective battery pack, which is then tested before shipping. Needless to say, the process of selecting matching cells and subsequently testing the assembled battery packs increases the time and cost of manufacturing the battery packs.
Despite the safeguards used to protect against faulty battery packs, as discussed above, the use of battery packs in electronic devices and systems still pose undesirable risks and hazards. For example, in many consumer products, although a battery pack used to power the product may be in good working condition when initially purchased, over time, one or more cells in the battery pack may degrade more rapidly than other cells in the pack, which could unduly degrade the performance of the entire battery pack, or cause a catastrophic failure of the battery pack (e.g., a fire).
As another example, for many consumer products (e.g., a wireless IP camera) that utilize battery packs as a power source, consumers will often replace the original batteries with new batteries (e.g., rechargeable batteries). Doing so, however, poses an undesirable risk because the cells are not necessarily properly matched for series and/or parallel operation, and therefore there is risk of overheating or possibly even fire under certain fault conditions. Some exemplary fault conditions are discussed below with reference to FIG. 1.
FIG. 1 illustrates a block diagram of a conventional battery pack 100 having two batteries 102 and 104, designated as “Battery A” and “Battery B,” respectively, connected in parallel. As shown in FIG. 1, the negative terminals of each battery 102 and 104 are connected to electrical ground, and their positive terminals are each connected to PSYS, which designates a power node of an electrical device or system (not shown) powered by the battery pack 100. In this way, battery pack 100 provides power (i.e., voltage and current) to the electrical device or system.
An exemplary fault condition can occur if one of the batteries, e.g., battery 102 (Battery A), is defective or damaged such that it produces zero volts and/or becomes a short circuit. When a user inserts the second battery 104 (Battery B) into the battery pack, the first battery 102 (Battery A) can appear as an electrical short circuit that will cause a rapid discharge of the second battery 104 (Battery B) if no current limiting devices are installed and/or active in either battery 102 or 104. The result can be extremely high currents that can generate extreme heat and possibly cause a fire or explosion, in addition to diminishing the life of the second battery 104 (Battery B). This is a relatively common failure of Lithium type cells that should be avoided.
As another example of a fault condition, if the first battery 102 (Battery A) is good, but has lower voltage than the second battery 104 (Battery B) when installed, this could also result in an unrestricted current flow from the second battery 104 (Battery B) to the first battery 102 (Battery A). As discussed above, such a high current flow may be hazardous (e.g., cause a fire), as well as being detrimental to the life of the first battery 102 (Battery A), as the unrestricted current can exceed recommended operating parameters.
As a further example, if the first battery 102 (Battery A) and the second battery 104 (Battery B) are made from different technologies, such as Li-Ion and Li—FePO4 technologies, for example, which most consumers do not understand, this condition can again result in batteries having different voltages and consequently higher than normal operating currents as the battery pack circuit 100 tries to equalize their voltages. The high currents can lead to dangerously high temperatures and/or a fire, in addition to significantly diminishing the life of the battery pack.
In view of the above exemplary problems associated with prior art battery packs and their use in electronic devices and systems, there is a need for a method and apparatus for safeguarding against one or more mismatched, degraded or damaged batteries in a battery pack.